System and method for apodization in a semiconductor device inspection system

ABSTRACT

An inspection system with selectable apodization includes an illumination source configured to illuminate a surface of a sample, a detector configured to detect at least a portion of light emanating from the surface of the sample, the illumination source and the detector being optically coupled via an optical pathway of an optical system, a selectably configurable apodization device disposed along the optical pathway, wherein the apodization device includes one or more apodization elements operatively coupled to one or more actuation stages configured to selectably actuate the one or more apodization elements along one or more directions, and a control system communicatively coupled to the one or more actuation and configured to selectably control apodization of illumination transmitted along the optical pathway by controlling an actuation state of the one or more apodization elements.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is related to and claims the benefit of theearliest available effective filing date(s) from the following listedapplication(s) (the “Related Applications”) (e.g., claims earliestavailable priority dates for other than provisional patent applicationsor claims benefits under 35 USC §119(e) for provisional patentapplications, for any and all parent, grandparent, great-grandparent,etc. applications of the Related Application(s)).

Related Applications:

-   -   For purposes of the USPTO extra-statutory requirements, the        present application constitutes a regular (non-provisional)        patent application of United States Provisional Patent        Application entitled System and Method For Apodization In A        Semiconductor Inspection System, naming Jamie Sullivan, Gary        Janik, Steve Cui, Rex Runyon, Dieter Wilk, Steve Short, Mikhail        Haurylau, Qiang Q. Zhang, Grace Hsiu-Ling Chen, Robert Danen,        Suwipin Martono, Shobhit Verma, Wenjian Cai, Meier Brender as        inventors, filed Feb. 10, 2012, Application Ser. No. 61/597,459.

TECHNICAL FIELD

The present invention generally relates to a method and system forimplementing a selected apodizing function, and, in particular, a methodand system for selectably implementing an apodizing function.

BACKGROUND

Fabricating semiconductor devices such as logic and memory devicestypically includes processing a substrate such as a semiconductor waferusing a large number of semiconductor fabrication processes to formvarious features and multiple levels of the semiconductor devices.Examples of semiconductor fabrication processes include, but are notlimited to, lithography, chemical-mechanical polishing, etch,deposition, and ion implantation. Multiple semiconductor devices may befabricated in an arrangement on a single semiconductor wafer and thenseparated into individual semiconductor devices.

As the dimensions of semiconductor devices decrease, the demand forimproved inspection processes and tools increases. Inspection processesare used at various steps during a semiconductor manufacturing processto detect defects on wafers, leading to increased device yield. Manydifferent types of inspection tools have been developed for theinspection of semiconductor wafers. Defect inspection is currentlyperformed using techniques such as bright field (BF) imaging, dark field(DF) imaging, and scattering. The type of inspection tool that is usedfor inspecting semiconductor wafers may be selected based on, forexample, characteristics of the defects of interest and characteristicsof the wafers that will be inspected. For example, some inspection toolsare designed to inspect unpatterned semiconductor wafers or patternedsemiconductor wafers.

Patterned wafer inspection is of particular interest and importance tothe semiconductor industry because processed semiconductor wafersusually have a pattern of features formed thereon. Inspection ofpatterned wafers is, therefore, important to accurately detect defectsthat may have been formed on the wafer during, or as a result of,processing.

Many inspection tools have been developed for patterned waferinspection. For example, patterned wafer inspection tools commonlyutilize spatial filters to enhance patterned wafer inspection. Thesespatial filters may include, but are not limited to, Fourier filters andapodizing filters.

Since the light scattered from patterned features depends on variouscharacteristics of the patterned features such as lateral dimension andperiod, the design of the spatial filter also depends on suchcharacteristics of the patterned features. As a result, the spatialfilter must be designed based on known or determined characteristics ofthe patterned features and must vary as different patterned features arebeing inspected. Therefore, it is desirable to provide a system andmethod that cures the defects of the prior art.

SUMMARY

An inspection system for providing selectable apodization is disclosed.In a first aspect, the system may include, but is not limited to, anillumination source configured to illuminate a surface of a sampledisposed on a sample stage; a detector configured to detect at least aportion of light emanating from the surface of the sample, theillumination source and the detector being optically coupled via anoptical pathway of an optical system including an illumination arm and acollection arm; a selectably configurable apodization device disposedalong the optical pathway of the optical system, wherein the apodizationdevice includes one or more apodization elements operatively coupled toon one or more actuation stages, the one or more actuation stagesconfigured to selectably actuate the one or more apodization elementsalong one or more directions; a control system communicatively coupledto the one or more actuation stages, wherein the control system isconfigured to selectably control apodization of illumination transmittedalong the optical pathway of the optical system in one or moredirections by controlling an actuation state of the one or moreapodization elements.

An inspection system for providing apodization is disclosed. In a firstaspect, the system may include, but is not limited to, an illuminationsource configured to illuminate a surface of a sample disposed on asample stage; a detector configured to detect at least a portion oflight emanating from the surface of the sample; an optical systemincluding an optical pathway configured to optically couple theillumination source and the detector; and a serrated aperture assemblydisposed along the optical pathway of the optical system and configuredas an aperture of the optical system, the serrated aperture assemblyincluding one or more serrated aperture stops, wherein the one or moreserrated aperture stops including a plurality of serration featuresconfigured to apply an apodization profile to illumination transmittedthrough an aperture of the one or more serrated aperture stops, the oneor more serrated aperture stops including a serrated pattern having aselected orientation.

An inspection system for providing spatial filtering is disclosed. In afirst aspect, the system may include, but is not limited to, anillumination source configured to illuminate a surface of a sampledisposed on a sample stage; a detector configured to detect at least aportion of light emanating from the surface of the sample; an opticalsystem including an optical pathway configured to optically couple theillumination source and the detector, the optical pathway including anillumination arm and a collection arm; a Fourier filter disposed alongthe optical pathway of the optical system, wherein the Fourier filterincludes one or more illumination blocking elements arranged in an arraypattern, wherein the one or more illumination blocking elements arearranged to block a portion of illumination from the sample, wherein oneor more edge regions of the illumination blocking elements have agraduated transmission function, wherein a locally averaged transmissionfunction of the Fourier filter is an apodizing function.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not necessarily restrictive of the invention as claimed. Theaccompanying drawings, which are incorporated in and constitute a partof the specification, illustrate embodiments of the invention andtogether with the general description, serve to explain the principlesof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The numerous advantages of the disclosure may be better understood bythose skilled in the art by reference to the accompanying figures inwhich:

FIG. 1A is a simplified schematic view of a system for providingselectable apodization in a brightfield inspection system, in accordancewith one embodiment of the present invention.

FIG. 1B is a simplified schematic view of a system for providingselectable apodization in a darkfield inspection system, in accordancewith one embodiment of the present invention.

FIG. 1C is a schematic view of a section of a circular variable dotpattern density apodization element, in accordance with one embodimentof the present invention.

FIG. 2A is an intensity versus numerical aperture graph illustrating theintensity as a function of NA for an unapodized pupil and an apodizedpupil, in accordance with one embodiment of the present invention.

FIG. 2B is a log scale graph depicting the point spread function for anunapodized pupil and an apodized pupil, in accordance with oneembodiment of the present invention.

FIG. 2C is a linear scale graph depicting the point spread function foran unapodized pupil and an apodized pupil, in accordance with oneembodiment of the present invention.

FIG. 2D is a linear scale graph depicting the point spread function foran unapodized pupil and an apodized pupil used to identify the firstdark ring, in accordance with one embodiment of the present invention.

FIG. 2E is an intensity versus numerical aperture graph depictingintensity as a function of numerical aperture for various apodizationprofiles, in accordance with one embodiment of the present invention.

FIG. 2F is a linear scale graph depicting the point spread function forvarious apodization profiles, in accordance with one embodiment of thepresent invention.

FIG. 3A is a simplified schematic view of a brightfield inspectionsystem with a serrated aperture stop, in accordance with one embodimentof the present invention.

FIG. 3B is a schematic view of a serrated aperture stop, in accordancewith one embodiment of the present invention.

FIG. 3C is a schematic view of two serrated aperture stops in a stackedconfiguration to form a composite aperture, in accordance with oneembodiment of the present invention.

FIG. 3D is a schematic view of a diffraction pattern resulting from theapplication of a serrated aperture stop, in accordance with oneembodiment of the present invention.

FIG. 3E is a schematic view of the positioning of the imaging portion ofa detector to avoid the diffraction pattern resulting from theapplication of a serrated aperture stop, in accordance with oneembodiment of the present invention.

FIG. 3F is a schematic view of a serrated aperture stop with truncatedserration features along one direction, in accordance with oneembodiment of the present invention.

FIG. 3G is a schematic view of a diffraction pattern resulting from theapplication of a serrated aperture stop with truncated serrationfeatures along one direction, in accordance with one embodiment of thepresent invention.

FIG. 4A is a simplified schematic view of a darkfield inspection systemequipped with a Fourier filter having apodized edges, in accordance withone embodiment of the present invention.

FIG. 4B is a simplified schematic view of a brightfield inspectionsystem equipped with a Fourier filter having apodized edges, inaccordance with one embodiment of the present invention.

FIG. 4C is a schematic view of a Fourier filter having blocking elementswith apodized edges suitable for implementation in the collection arm ofan inspection system, in accordance with one embodiment of the presentinvention.

FIG. 4D is a schematic view of a variable dot density edge of a blockingelement of a Fourier filter, in accordance with one embodiment of thepresent invention.

FIG. 4E is a schematic view of a graded coating edge of a blockingelement of a Fourier filter, in accordance with one embodiment of thepresent invention.

FIG. 4F is a schematic view of a Fourier filter having apodized edgessuitable for implementation in the illumination arm of an inspectionsystem, in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the subject matter disclosed,which is illustrated in the accompanying drawings.

Referring generally to FIGS. 1A through 4F, systems and methods forimplementing apodization in an optical pathway of an optical inspectionsystem are described in accordance with the present disclosure.

The present invention is generally directed to methods and systems forproviding apodization of illumination transmitted along an opticalpathway of an inspection system used in the optical inspection of asample, such as semiconductor wafer. Generally, apodization includes themodification of the amplitude transmittance of an aperture of an opticalsystem in order to reduce diffraction effects. In the case of a circularaperture, apodization may consist of modifying the transmittance of theaperture in order to reduce or suppress the energy in the diffractionrings (relative to that of the central Airy disk). In the case of anon-circular aperture, the diffraction point spread function at anoptical system's focal plane will not possess the form of an Airypattern, but it will generally exhibit diffraction tails extendingoutside of the central diffraction peak as a result of diffraction atthe aperture. For example, Born et al. describes apodization generallyin Chapter 8 of Principles of Optics, 6th Ed., (1980), which isincorporated herein by reference in the entirety. The diffraction tailsare commonly associated with the high spatial frequency component oftwo-dimensional transmittance profile of the aperture. The high spatialfrequency component originates primarily from the sharp transmittancediscontinuities at the aperture edges, and the diffraction tails can besuppressed by modifying the amplitude transmittance of the aperture,thereby mitigating these discontinuities. An aperture transmittancefunction which achieves this suppression of diffraction effects isreferred to herein as an “apodization profile” or “apodizationfunction.” Common apodization functions include, but are not limited to,truncated Gaussian profiles and cosine profiles. The followingdisclosure provides multiple embodiments of methods and systems suitablefor applying apodization to illumination transmitted along an opticalpathway of an inspection system.

In addition, it is noted herein that patterned bus regions ofsemiconductor devices of a wafer are commonly very bright relative towell filtered array areas and unpatterned regions of the devices.Inspection tools are typically able to find much smaller defects inthese well filtered array and unpatterned regions because less nuisancelight is reflected or scattered from a pattern.

Unintentional optical artifacts in these quite regions can limit thesensitivity of wafer inspection tools as these artifacts may result infalse defects or increased noise levels. Optical artifacts can resultfrom a number of sources including, but not limited to, diffraction fromoptical apertures. Diffraction can occur as a result of filteringmechanisms (e.g., Fourier filters) placed at the Fourier plane and usedto filter diffraction orders from repetitive features. Diffractionartifacts can also occur from the limiting system apertures. In thissetting bright features can “ring” into the unpatterned or well filteredarray regions, limiting inspection sensitivity. The present invention isfurther directed to methods and systems for reducing optical artifactsor ringing from optical apertures of an inspection system.

FIG. 1A illustrates a simplified schematic view of an inspection system100 with selectable apodization, in accordance with one embodiment ofthe present invention. The present invention is directed to a system andmethod providing a flexible means for enhancing resolution of an opticalmeasurement system, such as an inspection system. It is recognizedherein that apodization applied in a given setting may be selected basedon one or more sample features (e.g., device pattern features). As such,the present invention provides an inspection system equipped withselectable apodization, allowing a user to either manually orautomatically implement a selected apodization profile in response toone or more sample features. It is further noted that the presentinvention allows for the selectable apodization of illumination alongtwo directions independently (e.g., X-direction and Y-direction).

In one aspect of the present invention, the system 100 includes anillumination source 102 configured to illuminate a surface of a sample106 (e.g., semiconductor wafer) disposed on a sample stage 108, adetector 104 (e.g., CCD, TDI, or PMT detector) configured to detectlight emanating (e.g., scattered or reflected) from the surface of thesample 106. The illumination source 102 (e.g., broadband source ornarrowband source) and the detector 104 are optically coupled via anoptical pathway 109 of an optical system 111. In another aspect, thesystem 100 includes a selectably configurable apodization device 107disposed along the optical pathway 109 of the optical system 111 of theinspection system 100. The system 100 may further include a controlsystem 114 (e.g., computer control system equipped with one or moreprocessors 116) communicatively coupled to the selectably configurableapodization device 107 and suitable for selectably controlling theapodization applied to illumination transmitted along the opticalpathway 109 and through the apodization device 107.

In a further aspect of the present invention, the selectablyconfigurable apodization device 107 may include one or more apodizationelements 103 operatively coupled to on one or more actuation stages 105.In this regard, the one or more actuation stages 107 are configured toselectably actuate the one or more apodization elements 103 along one ormore directions (e.g., X-direction or Y-direction). The control system114 may be communicatively coupled to the one or more actuation stages103 of the apodization device 107, thereby allowing the control system114 to selectably control apodization (e.g., apply a selectedapodization profile along a first and/or second direction) ofillumination transmitted along the optical pathway 109 of the opticalsystem in one or more directions by controlling an actuation state(e.g., positioned within optical pathway or positioned outside ofoptical pathway) of the one or more apodization elements 103.

In another aspect of the present invention, the optical pathway 109 ofthe optical system 111 may include an illumination arm 110 and acollection arm 112. In this manner, the illumination source 102 and thedetector 104 may be optically coupled via the illumination arm 110 andthe collection arm 112 of the optical system 111. Light may emanate fromthe illumination source 102 and travel along the illumination arm 110 tothe surface of the sample 106. Light scattered or reflected from thesample 106 may then travel from the surface of the sample 106 to thedetector 104 along the collection arm 112.

In one embodiment, the apodization device 107 is disposed along theillumination arm 110 of the optical system 111 of the inspection system100, as shown in FIG. 1A. In an alternative embodiment, although notshown in FIG. 1A, the apodization device 107 is disposed along thecollection arm 112 of the optical system 111 of the inspection system100.

The inspection system of the present invention may be configured as anyinspection system known in the art. For example, as shown in FIG. 1A,the inspection system 100 of the present invention may be configured asa bright field (BF) inspection system. Alternatively, as shown in FIG.1B, the inspection system 100 of the present invention may be configuredas a dark field (DF) inspection system. Applicant notes that the opticalconfigurations depicted in FIGS. 1A and 1B are provided merely forillustrative purposes and should not be interpreted as limiting. In ageneral sense, the inspection system 100 of the present invention mayinclude any set of imaging and optical elements suitable for imaging thesurface of the wafer 106. Examples of currently available waferinspection tools are described in detail in U.S. Pat. No. 7,092,082,U.S. Pat. No. 6,702,302, U.S. Pat. No. 6,621,570 and U.S. Pat. No.5,805,278, which are each herein incorporated by reference. In addition,various embodiments of combination BF and DF inspection systems areprovided in U.S. Pat. No. 5,822,055 and U.S. Pat. No. 6,201,601, whichare each incorporated herein by reference in their entirety.

In additional embodiments, the illumination arm 110 and/or thecollection arm 112 may include, but are not limited to, one or moreadditional optical elements as those skilled in the art should recognizethat numerous optical elements may be utilized within the illuminationarm 110 or collection arm 112 within the scope of the present invention.For example, in the case of the brightfield inspection system shown inFIG. 1A, the additional optical elements of the illumination arm 110 mayinclude, but are not limited to, one or more condenser or focusinglenses 101, one or more objective lenses 122, one or more additionallenses, one or more beam splitters 114, one or more mirrors, one or morefilters, one or more collimators and the like. Similarly, the opticalelements of the collection arm 112 may include, but are not limited to,one or one or more imaging lenses 124, one or more additional lenses,one or more mirrors, one or more filters, or one or more collimators andthe like.

In the case of the darkfield inspection system shown in FIG. 1A, theadditional optical elements of the illumination arm 110 may include, butare not limited to, one or more focusing or condenser lenses 101, one ormore additional lenses, one or more beam splitters (not shown), one ormore mirrors, one or more filters, one or more collimators and the like.Similarly, the optical elements of the collection arm 112 may include,but are not limited to, one or more collection lenses 123, one or moreimaging lenses 124, one or more additional lenses, one or more mirrors,one or more filters, or one or more collimators and the like. It isnoted herein that the above described optical systems for the darkfieldand brightfield embodiments of the inspection system 100 should not beinterpreted as limiting. It is recognized herein that any implementingoptical system will include additional optical elements not describedherein. Applicant notes that the various additional elements wereomitted from the present description for the purposes of clarity.

It is noted herein that while the following description of the presentinvention describes the inspection system 100, it is recognized hereinthat the apodization device 107 may be implemented in optical system notdisclosed herein. As such, the particular optical configuration ofsystem 100 should not be interpreted as limiting.

In another aspect of the present invention, the Illumination source 102may include any broadband illumination source known in the art. In oneembodiment, the illumination source 102 may include, but is not limitedto, a halogen light source (HLS). For instance, the halogen light sourcemay include, but is not limited to, a tungsten based halogen lamp. Inanother example, the illumination source 102 may include a xenon arclamp. By yet another example, the illumination source 102 may include adeuterium arc lamp. In a general sense, any illumination source capableof producing illumination in the visible, infrared, and ultravioletspectral ranges is suitable for implementation in the present invention.For example, a xenon arc lamp is capable of delivering light in aspectral range of 190 nm to 2000 nm, with a gradual radiant intensitydecrease below 400 nm. In another embodiment, the illumination source102 may include, but is not limited to, any discharge plasma sourceknown in the art. In yet another embodiment, the illumination source 102may include, but is not limited to, a laser-driven plasma source. Itshould be recognized by those skilled in the art that the abovedescribed illumination sources do not represent limitations, but shouldmerely be interpreted as illustrative. In an additional aspect of thepresent invention, the illumination source 102 may include anynarrowband illumination source known in the art. For example, theillumination source 102 may include, but is not limited to, one or morelaser light sources.

It is noted that the above description relating to the various types ofillumination sources should not be interpreted as limiting, but rathermerely as illustrative. Those skilled in the art should recognize thatany broadband or narrowband illumination source is suitable forimplementation in the present invention. Moreover, it is furthercontemplated herein that two or more illumination source may be combinedin order to achieve a required spectral range. In this manner, a firstsource emitting illumination in a first spectral range may be combinedwith a second source emitting illumination in a second spectral range.For example, a first light source may include a xenon lamp, while asecond light source may include a deuterium lamp.

In another aspect of the present invention, the detector 104 may includeany optical detection system known in the art suitable for imaging oneor more features of the surface of the sample 106. In one embodiment,the detector 104 may include, but is not limited to, a CCD detector. Inanother embodiment, the detector 104 may include, but is not limited to,CCD-TDI detector. In another embodiment, the detector 103 may includebut is not limited to, a PMT detector. In an additional embodiment, thedetector 104 (e.g., imaging camera) may be communicatively coupled to animage processing computer which may identify and store imagery dataacquired from the detector 104.

Referring now to the selectably configurable apodization device 107 ofFIGS. 1A and 1B, the selectably configurable apodization device 107 mayinclude any apodization element (e.g., apodizer) and actuation stageknown in the art. For example, the selectably configurable apodizationdevice 107 may include an apodization element 103 mechanically coupledto a linear translation stage (e.g., linear motorized stage). In thisregard, the apodization element 103 is configured for the selectivelinear translation in to and out of the optical pathway 109 of theoptical system 111 in response to a command signal received from thecontrol system 114. By way of another example, the selectablyconfigurable apodization device 107 may include an apodization element103 mechanically coupled to a rotational stage (e.g., motorizedrotational stage). In this regard, the apodization element 103 isconfigured for the selective rotation in to and out of the opticalpathway 109 of the optical system 111 in response to a command signalreceived from the control system 114. By way of another example, theselectably configurable apodization device 107 may include anapodization element 103 mechanically coupled to a combinationtranslational-rotational stage. In this regard, the apodization element103 is configured for the selective rotation and/or translation in toand out of the optical pathway 109 of the optical system 111 in responseto a command signal received from the control system 114.

In another aspect of the present invention, the selectably configurableapodization device 107 may include multiple apodizing elements, witheach apodizing element 103 disposed on an individual actuation stage(e.g., translational stage or rotational stage). In this regard, theapodization device 107 may include a battery of apodizing elements 103,whereby the control system 114 is configured to selectably actuate aselected sub-set of the apodizing elements 103 into the optical pathway109 of the inspections system 100 via the corresponding actuation stages105 in order to achieve a selected apodization profile. In this regard,the selected apodization profile is formed using the combination ofmultiple apodizing elements.

For example, the control system 114 may selectably actuate a singleapodizing element 103 into the optical pathway 109 via its correspondingactuation stage 105. By way of another example, the control system 114may selectably actuate two or more apodizing elements 103 into theoptical pathway 109 via their corresponding actuation stages 105. It isrecognized herein that the choice of apodizing element 103 to beactuated into the optical pathway 109 may depend on the apodizingcharacteristics required of the inspection system (e.g., based onpattern features of sample) as well as the pre-loaded apodizing elements103 of the apodization device 107.

It is noted herein that any apodizing element or filter is suitable forimplementation in the apodization device 107 of the present invention.In one embodiment, the one or more apodizing elements 103 of theapodization device 107 may include a variable dot density patternelement. FIG. 1C illustrates a segment of a variable dot density patternelement 130 configured for a circular aperture, in accordance with oneembodiment of the present invention.

In one embodiment, the variable dot density based apodizing element 130may include substantially opaque features 132, or “dots,” on asubstantially transparent background 134, whereby the density of thefeatures varies as a function of the radial position on the apodizingelement 130, as shown in FIG. 1C. In a further embodiment, the variabledot density pattern based apodizing element 103 may have a locallyaveraged transmittance function that is an apodizing function. In thisregard, rather than a sharp transition from near 100% transmission to 0%transmission (e.g., typical microscope iris), the limiting aperture ofthe present embodiment may be lithographically printed with a series ofopaque features of varying density. Further, in cases where the dotfeatures are very dense, as is the case for the edge of the aperture,the transmission is very low. In contrast, when the density of featuresis very low as is the case for the center of the aperture 134, thetransmission is very high. As shown in FIG. 1C, these varying featuredensity along the transition region 133 provides a smooth transitionfrom the clear central part of the optical aperture 134 to the zerotransmission limiting diameter position 131.

In an alternative embodiment, the variable dot density based apodizingelement may include a “negative” version of the embodiment depicted inFIG. 1C. In this sense, the apodizing element 130 may includesubstantially transparent features on a substantially opaque background,whereby the density of the features varies as a function of the radialposition on the apodizing element 130. It is recognized herein that thevariable dot density apodizing elements 130 and random dot densityapodizing elements of the present invention may be fabricated using anymeans known in the art. For example, the variable dot pattern or randomdot pattern may be formed utilizing a lithographic printing,evaporation, and/or etching process. For instance, the opaque featuresof the apodizing element 130 (and negative version of element 130) maybe lithographically printed onto a glass substrate. For instance, theopaque features may be formed from a metal material (e.g., chrome)deposited onto a substrate (e.g., glass substrate or quartz glasssubstrate). Applicants note that the above description of the variabledot density pattern is not limiting and is provided merely forillustration. It is anticipated that numerous geometrical configurationsof the variable dot density element are suitable for implementation inthe present invention. For example, it is noted herein that the dots ofthe dot density pattern are not limited to circles. The dots of thevariable dot density pattern may include any geometrical shape known inthe art, such as, but not limited to, rectangles, circles, ellipses,rings and the like.

In another embodiment, the one or more apodizing elements 103 of theapodization device 107 may include a spatially varying neutral densityfilter (not shown). U.S. Pat. No. 5,859,424 to Norton et al. describesthe construction of individual apodizing filters (e.g., variable dotfilters and neutral density filters) suitable for implementation in theapodization device 107 of the present invention and is incorporatedherein by reference in the entirety.

In a further embodiment, the apodization device 107, when configuredwith the dot density (variable or random) or neutral coating densityapodizing elements described above, may be positioned at any point alongthe optical pathway 109. In this regard, the apodization device 107 maybe placed along the illumination arm 110 or the collection arm 112. Forexample, in the case of BF and/or DF inspection, the apodization device107 may be positioned such that the active apodization element(s) 103 ofthe device 107 act as the limiting aperture stop (e.g., the illuminationaperture stop) of the illumination arm 110, as conceptually shown inFIGS. 1A and 1B respectively. By way of another example, in the case ofBF inspection, the apodization device 107 may be positioned at theimaging aperture stop of the collection arm 110, located prior to theimaging lens 124. By way of another example, in the case of DFinspection, the apodization device 107 may be positioned at the imagingaperture stop of the collection arm 110, located between the collectionlens 123 and the imaging lens 124.

In another embodiment, the one or more apodizing elements 103 of theapodization device 107 may include, but are not limited, one or moreserrated aperture stops configured as an aperture of the inspectionsystem 100 and configured to apply an apodized pupil function. In thisregard, when configured with a serrated aperture stop, the one or moreapodization devices 107 may be positioned along the optical path 109 soas to serve as the aperture stop of the imaging system of the opticalsystem 109. It is recognized herein that the imaging system of theoptical system may reside in either the illumination arm 110 or thecollection arm 112 of the inspection system 100. For example, the one ormore apodizing elements 103 may consist of, but are not limited to, theserrated aperture stops described further herein and illustrated inFIGS. 3B, 3C, and 3F.

In another embodiment, the one or more apodizing elements 103 of theapodization device 107 may include, but are not limited, one or moreFourier filtering elements with edge apodization. In this regard, whenconfigured with a Fourier filtering element, the one or more apodizationdevices 107 may be positioned along the optical path 109 so as toprovide Fourier filtering of diffracted or reflected from patternedfeatures from the sample. For example, when in a Fourier filteringconfiguration, the apodization device 107 may be positioned at theFourier plane of the imaging system of the optical system 109. Forinstance, the apodization device 107 may be positioned at the Fourierimaging plane of the collection arm 112. For example, the one or moreapodizing elements 103 may consist of, but are not limit to, the Fourierfilter having one or more blocking elements with edge apodizationdescribed further herein and illustrated in FIGS. 4A-4F.

In one aspect of the present invention, the control system 114 mayinclude one or more processors 116 communicatively coupled to theselectably configurable apodization device 107, as shown in FIGS. 1A-1B.For example, the one or more processors 116 of the control system 114may be communicatively coupled to the one or more actuation stages 105of the selectably configurable apodization device 104. In this regard,the control system 114 may consist of a computing system configured tocontrol the selectably configurable apodization device 107 in order toachieve a selected apodization profile (as discussed throughout thepresent invention). In one embodiment, the one or more processors 116 ofthe control system 114 may act to configure the selectably configurableapodization device 107 into a selected apodization mode or state,thereby applying a selected apodization profile to illuminationtransmitted through the one or more apodizing elements 103.

In one embodiment, the apodization profile implemented by the one ormore processors 116 of the control system 114 is a function of one ormore patterns of the sample 106 being inspected by the inspection system100. For example, in settings where a sample has a high DR, the one ormore processors 116 of the control system 114 may apply an aggressiveapodization profile (by actuating the corresponding apodization elements103 need to achieve the aggressive profile) to illumination passingthrough the apodizing elements 103 of the selectably configurableapodization device 107. By way of another example, in settings where asample has a low DR, the one or more processors 116 of the controlsystem 114 may act to reduce the apodization by directing the one ormore actuation stages 105 to withdraw one or more of the apodizingelement 103 from the optical pathway 109.

In another embodiment, the one or more processors 116 of the controlsystem 114 may selectably control apodization of illumination along afirst direction and a second direction independently. For example, theone or more processors 116 of the control system 114 may direct theapodization device 107 to apply apodization to the X and Y axesindependently. For instance, the amount of apodization applied maydepend on the geometry of a layout of an inspected IC chip of the sample106. Further, it is noted herein that for rectangular peripheralstructures it may be desirable to apply only X apodization, while inother settings it may be desirable to apply only Y apodization.

In another embodiment, the one or more processors 116 of the controlsystem 114 may selectably control apodization of illumination along theoptical pathway 109 in one or more directions (e.g., X-direction orY-direction) by controlling the actuation state of two or more actuationstages 105 of the selectably configurable apodization device 107. Forexample, a first apodization element may be disposed on a firstactuation stage of the apodization device 107, while a secondapodization element may be disposed on a second actuation stage of theapodization device 107. In this regard, the one or more processors 116of the control system 114 are configured to selectably control theapodization profile of illumination transmitted along the opticalpathway 109 of the optical system 111 in one or more directions bycontrolling an actuation state of the first apodization element and anactuation state of the second apodization element. It is noted hereinthat the above embodiment is not limited to two apodization elements. Itis recognized herein that any number of apodizing elements and stagesmay be implemented in the selectably configurable apodization device 107of the present invention. In addition, it is further noted that any typeof apodization element (as described throughout the present disclosure)may be included in the multiple apodizing element selectablyconfigurable apodization device 107 of the present invention.

In one embodiment, the one or more processors 116 of control system 114may receive user inputted instructions via a user interface 126. Inresponse to user inputted instructions, the one or more processors 116of the control system 114 may act to configure the selectablyconfigurable apodization device 107 into a selected apodization mode orstate. For example, the one or more processors 116 of control system 114may display a set of mode selections to a user via a display of the userinterface. The user may then select one or more of the selections via auser input device (not shown). In response to this selection, one ormore processors of the control system 114 may transmit control signalsto the selectably configurable apodization device 107 in order to directthe one or more actuation stages 105 to actuate (e.g., translate orrotate) the one or more apodization elements 103 into or out of theoptical pathway 109 in order to correspond with the user-selectedconfiguration.

In another embodiment, the one or more processors 114 are incommunication with a memory medium 118 (e.g., non-transitory storagemedium). In addition, the one or more memory media 118 may store theprogram instructions configured to cause the one or more processors 116to carry out the various steps described through the present disclosure.The memory medium 118 may include any memory medium known in the artincluding, but not limited to, a read-only memory, a random accessmemory, a magnetic or optical disk, or a magnetic tape. Programinstructions 120 implementing methods such as those described herein maybe transmitted over or stored on a carrier medium. The carrier mediummay be a transmission medium such as a wire, cable, or wirelesstransmission link. The carrier medium may also include a memory medium116 such as a read-only memory, a random access memory, a magnetic oroptical disk, or a magnetic tape.

In general, the term “processor” may be broadly defined to encompass anydevice having one or more processors, which execute instructions from amemory medium. In this sense, the one or more processors 116 may includeany microprocessor-type device configured to execute software algorithmsand/or instructions. In one embodiment, the one or more processors 116may consist of a desktop computer, a networked computer, an imagecomputer, a work station, a parallel processing computer, and the likeconfigured to execute a program configured to control the selectablyconfigurable apodization device 107 of the system 100, as describedthroughout the present disclosure. It should be recognized that thesteps described throughout the present disclosure may be carried out bya single computer system or, alternatively, multiple computer systems.Moreover, different subsystems of the system 100, such as the userinterface 126, the actuation stages 105, and the like, may include aprocessor or logic elements suitable for carrying out at least a portionof the steps described above. Therefore, the above description shouldnot be interpreted as a limitation on the present invention but merelyan illustration.

In another embodiment, the one or more processors 116 of the controlsystem 114 may be communicatively coupled to the selectably configurableapodization device 107, the illumination source 102, the detector 104,the user interface 126 or any other sub-system of system 100 in anymanner known in the art. For example, the one or more processors 116 ofthe control system 114 may be communicatively coupled to the varioussub-systems of system 100 via a wireline or wireless connection.

The user input device may include any user input device known in theart. For example, the user input device may include, but is not limitedto, a keyboard, a keypad, a touchscreen, a lever, a knob, a scrollwheel, a track ball, a switch, a dial, a sliding bar, a scroll bar, aslide, a handle, a touch pad, a paddle, a steering wheel, a joystick, abezel input device or the like. In the case of a touchscreen interfacedevice, those skilled in the art should recognize that a large number oftouchscreen interface devices may be suitable for implementation in thepresent invention. For instance, the display device may be integratedwith a touchscreen interface, such as, but not limited to, a capacitivetouchscreen, a resistive touchscreen, a surface acoustic basedtouchscreen, an infrared based touchscreen, or the like. In a generalsense, any touchscreen interface capable of integration with the displayportion of the display device is suitable for implementation in thepresent invention. In another embodiment, the user interface mayinclude, but is not limited to, a bezel mounted interface. In the caseof a bezel input device, the display device may include a bezel equippedwith one or more bezel mounted interface devices. For instance, thebezel mounted interface may include, but is not limited to, a hard key(or hard “button”) disposed on the bezel of the display device. In ageneral sense, any bezel mounted interface capable of integration withthe display device is suitable for implementation in the presentinvention.

The display device of the user interface 126 may include any displaydevice known in the art. In one embodiment, the display device mayinclude, but is not limited to, a liquid crystal display (LCD). Inanother embodiment, the display device 104 may include, but is notlimited to, an organic light-emitting diode (OLED) based display. Inanother embodiment, the display device 104 may include, but is notlimited to a CRT display. Those skilled in the art should recognize thata variety of display devices may be suitable for implementation in thepresent invention and the particular choice of display device may dependon a variety of factors, including, but not limited to, form factor,cost, and the like. In a general sense, any display device capable ofintegration with a user interface device (e.g., touchscreen, bezelmounted interface, keyboard, mouse, trackpad, and the like) is suitablefor implementation in the present invention.

It is recognized herein that while apodization of a pupil may lead toincreased resolution in some settings, apodization may also carry withit penalties that render the implementation of such apodizationundesirable. FIGS. 2A through 2F illustrate an analysis of opticalconditions that may exist when determining whether apodization isdesirable or undesirable.

FIG. 2A illustrates the transmission intensity profile of a cosineapodization filter 204 and the transmission intensity profile of anunapodized aperture 202. As shown in FIG. 2A, consider a 0.9 NA imagingsystem with a cosine profile applied from 0.45 NA to 0.9 NA. In thiscase, the pupil from 0 NA to 0.45 NA is unapodized, and, therefore,displays no attenuation. For a uniformly illuminated pupil, the regionfrom 0 NA to 0.45 NA only contains approximately 25% of the overallillumination. Most of the illumination (approximately 75%) is containedin the region where apodization is applied. In the case of a cosineapodizing profile (see curve 204) applied from 0.45 NA to 0.90 NA, mostof the illumination is blocked by the implemented apodizing filter. Inthis case, only 35% of the light from 0.45 NA to 0.90 NA is allowed topass through the implemented apodizing filter. Further, over the entireaperture from 0 NA to 0.9 NA, the optical system which is apodized from0.45 NA to 0.90 NA loses approximately 50% of the availableillumination. This represents a substantial apodizing filterimplementation penalty.

Similarly, apodization elements/filters act to broaden the width of thepoint spread function measured at moderate fractions of the peakamplitude. Again, consider a system with a uniform pupil distributionfrom 0 NA to 0.45 NA with cosine apodization applied from 0.45 NA to 0.9NA. Contrast this to a 0.9 NA optical system without apodization. Graph210 of FIG. 1B illustrates a log plot of the PSF 212 as a function ofPSF width for no apodization to the log plot of the PSF 214 for thecosine apodized setting described above. As shown in FIG. 2B, theapplication of the cosine apodizing filter acts to narrow the pointspread function when measured at small fractions of the peak amplitude.

FIG. 2C illustrates a linear plot 220 of the point spread function forthe apodized 222 and unapodized 224 configurations described above. Uponcloser inspection of the point spread function from approximately 1.0 to0.01, the PSF actually becomes wider upon adding the apodizationfunction.

It is noted herein that Lord Rayleigh's criterion for resolution foruniform pupil distribution (0.61·λ/NA) calculates the location of thefirst dark ring. Utilizing the same point spread functions describedabove, the location of the first dark ring for uniform pupildistribution from 0 NA to 0.9 NA with 266 nm light is found to beapproximately 0.00018 mm, which matches the Rayleigh criterion. Further,the first dark ring for the case with uniform apodization from 0 NA to0.45 NA and cosine apodization from 0.45 to 0.9 NA is at 0.00022 mm,which is 20% wider than the unapodized configuration. It is recognized,therefore, that apodization may narrow the point spread function whencontrol the tails of the point spread function is desirable, but it doesso at the expense of the PSF width at modest fractions of the peakintensity.

For small defects, the peak signal from the defects is generallyinversely proportional to square of the PSF width at moderate fractionsof the peak. As a result, the use of apodization filters results inlower signals from smaller defects. In this case, the width of the PSFin the tails is not important to the signal from the small defect. Inthe case of unapodized systems, the bulk of the PSF may be concentratedinto a smaller area. As a result, a higher fraction of the PSF interactswith the defect, which may lead to more scattered light for spotscanning imaging systems. In addition, it may result in more collectedlight focused onto fewer detector elements for a camera based imagingsystem. In both cases, the defect interacts with a larger fraction ofthe PSF. As a result of the broadening of the PSF, the signal will tendto decrease for apodized systems. While this may be a desirable tradeoff when these defects are in close proximity to very bright peripheralstructures, it is not likely a desirable tradeoff in cases where defectsare located in regions with little structure (e.g., bare areas and bulkarray) that benefit from increased light.

It is further noted herein that a broadening of the central point spreadfunction results in less resolution for logic regions. This behavior ineffect acts to stop down the NA in order to improve the transition fromvery bright regions to very dark regions, which tends to negativelyimpact logic inspection ability. Again consider a cosine apodizationfrom 0.45 to 0.9 NA. Such an apodization profile produced a first darkring with radius of 0.00022 mm. It is noted that the equivalentunapodized system that would produce the same dark ring position wouldpossess a NA of approximately 0.74.

Graph 240 of FIG. 2E illustrates a pupil function 244 for uniformapodization from 0 to 0.9 NA, a pupil function 242 for cosineapodization from 0.45 to 0.9 NA, and a pupil function 246 for uniformapodization from 0 to 0.74 NA.

Graph 250 of FIG. 2F illustrates PSF as function of PSF width 254 foruniform apodization from 0 to 0.9 NA, PSF as a function of PSF width 252for cosine apodization from 0.45 to 0.9 NA, and PSF as a function of PSFwidth 256 for uniform apodization from 0 to 0.74 NA. As shown in FIG.2F, the PSF for the “uniform from 0 to 0.45 NA and cosine apodized from0.45 to 0.9 NA” configurations possess a very similar PSF width whencompared to the “uniform 0 to 0.74 NA” configuration when measured atmoderate fractions of the peak.

As the various penalties above show, the analyzed pattern in questionhas a large impact on the decision as to whether apodization isdesirable. It is recognized that apodization may be advantageous whentrying to identify small defects in close proximity to very brightperipheral structures. In contrast, however, when the peripheralstructures are not significantly brighter than the bulk array of theanalyzed portion of the sample 106, the use of apodization and thecorresponding penalties may inhibit the ability of system 100 to finddefects.

For example, in the case where peripheral structures bordering arrayregions form a rectangular shape, it might be desirable to addapodization (using apodization device 107) to only a single axis.Similarly, if very bright vertical peripheral structures are presentalong with dim horizontal peripheral structures, a desired configurationmay include apodization to the vertical axis only, leaving thehorizontal axis unapodized.

In a general sense, it should be recognized that apodization of thepupil is not always desired. In this sense, the system 100 is configuredto apply apodization selectively and is further configured to controlthe degree of strength of apodization when, in fact, implemented.

FIGS. 3A-3B illustrate simplified schematic views of an inspectionsystem 300 equipped with a serrated aperture assembly 302 configured asan aperture of the optical pathway 109 of the inspection system 300, inaccordance with one embodiment of the present invention. The presentembodiment is directed to the improvement of resolution in an opticalinspection system (e.g., darkfield or brightfield inspection system). Inparticular, the present embodiment is directed to the enhancement ofsmall defect detection near bright peripheral structures. In the presentembodiment, improved system resolution is accomplished utilizingserrated aperture stops 304 configured as the aperture stop (e.g.,illumination aperture, imaging aperture, or another aperture) of theinspection system 300 to produce a desired apodizing function. It isfurther noted herein that in addition to improved resolution, thesoftening of the aperture edges may reduce the aperture placementaccuracy requirement. As a result, edge apodization may makesystem-to-system more straightforward.

It is recognized herein that the components and embodiments ofinspection system 100 described previously herein should be interpretedto extend to inspection system 300 unless otherwise noted. In thissense, the inspection system 300 includes an illumination source 102configured to illuminate a surface of a sample 106 disposed on a samplestage 108, a detector 104 configured to detect light emanating (e.g.,scattered or reflected) from the surface of the sample 106. Further, theillumination source 102 (e.g., broadband source or narrowband source)and the detector 104 are optically coupled via an optical pathway 109 ofan optical system 111.

In another aspect, the system 300 includes a serrated aperture assembly302 disposed along the optical pathway 109 of the optical system 111 andconfigured as an aperture of the inspection system 300. In anotheraspect, the serrated aperture assembly 302 may include one or moreserrated aperture stops 304, as shown in FIG. 3B. In one embodiment, theone or more serrated aperture stops 304 may be implemented as anillumination aperture stop. In this regard, the one or more serratedaperture stops 304 of the serrated aperture assembly 302 may be disposedalong the illumination arm 110 and configured to pass a selected amountof light from the illumination source 102 to the surface of the sample106. In another embodiment, the one or more serrated aperture stops 304may be implemented as an imaging aperture stop. In this regard, the oneor more serrated aperture stops 304 of the serrated aperture assembly302 may be disposed along the collection arm 112.

The one or more serrated aperture stops 304 may include a serratedaperture 306 formed by a plurality of serration features 308 arrangedabout the aperture 306. The serrated aperture features are formed in amanner (e.g., pitch, size, and etc.) such that the serrated aperture 306applies an apodization profile to illumination passing through theserrated aperture 306. In this regard, the one or more serrated aperturestops 304 may produce an apodized pupil function of illumination fromillumination source 102.

The one or more serrated aperture stops 304 of the presented inventionmay be formed in any manner known in the art. In one embodiment, the oneor more serrated aperture stops 304 are formed from a sheet metal plate.For example, a selected serrated aperture 306 may be cut out of a sheetmetal plate in such a manner to form the serrated aperture stop 306 asshown in FIG. 3B. In another embodiment, the one or more serratedaperture stops 304 are formed by depositing a patterned layer of metalmaterial (e.g., metal material opaque to illumination emitted byillumination source) onto a transparent substrate. For example, themetal used to form the patterned layer may include, but is not limitedto, chrome. In a further embodiment, a patterned layer of chrome may bedeposited onto any transparent (i.e., transparent to the illuminationemitted by the illumination source) substrate known in the art. Forexample, the transparent substrate may include, but is not limited to, aglass substrate or a quartz-glass substrate.

In another embodiment, the patterned metal layer may be deposited ontothe transparent substrate in any manner known in the art. For example,the patterned metal material may be deposited onto the substrate using aprinting process. By way of another example, the patterned metalmaterial may be deposited onto the substrate using an evaporationdeposition process.

In another embodiment, the one or more serration features 308 of the oneor more serrated aperture stops 304 may have a selected pitch. In afurther embodiment, the selected pitch may be selected based on theaspect ratio of the imaging portion of the detector 104.

In one embodiment, the serrated aperture assembly 102 may include asingle serrated aperture stop 304. In this regard, the arrangement ofthe serrated pattern features 308 of the single aperture stop may besuch to produce the desired pupil apodization function. In this sense, asingle serrated aperture stop 304 having serrated features 308 with asize, pitch, and position appropriate to produce the desired pupilapodization function may be implemented.

As shown in FIG. 3C, the serrated aperture assembly 302 may include twoor more serrated aperture stops 304 a and 304 b. In a furtherembodiment, the two or more serrated aperture stops may include a firstserrated aperture 304 a and a second serrated aperture stop 304 b. Inone embodiment, the first serrated aperture 304 a and the at least asecond serrated aperture stop 304 b may be “stacked” or coupled togetherto form a composite serrated aperture stop, as shown in FIG. 3C.

In this regard, the first serrated aperture stop 304 a is oriented withrespect to the at least a second serrated aperture stop 304 b in orderto form a composite aperture 307. In one aspect, the composition patternformed by the interleaving of the first set of serrated features 308 aand the second set of serrated features 308 b may act to achieve aselected pitch. In another aspect, the composition pattern formed by theinterleaving of the first set of serrated features 308 a and the secondset of serrated features 308 b may act to achieve the desiredapodization profile. It is recognized herein that a multiple serratedaperture stop approach may aid in mitigating fabrication difficulties asit allows a user to more readily achieve a desired pitch and compositepattern feature.

In another embodiment, the one or more serrated apertures stops 304 ofthe serrated aperture assembly 302 may be selectably inserted into theoptical pathway 109 of the inspection system 300. In this regard, theone or more serrated aperture stops 304 are selectably actuatable alonga direction substantially perpendicular to the optical pathway 109. Inone embodiment, the one or more serrated aperture stops 304 are disposedon an actuation stage (not shown) (e.g., translation stage and/orrotational stage) suitable for selectable placing the one or moreserrated apertures into the illumination arm 110 or the collection arm112 of the inspection system 300. In this regard, a control system maybe communicatively coupled to the actuation stage and configured toselectably control the placement of the one or more serrated aperturestops 304. For example, the control system used to control theapodization imparted by the serrated apertures 306/307 may consist ofthe control system 114 described previously herein.

In another embodiment, the one or more serrated aperture stops 304 aredisposed on a slidable stage (not shown) (e.g., translation stage and/orrotational stage) suitable for selectably placing the one or moreserrated apertures into the illumination arm 110 or collection arm 112of the inspection system 300. In this regard, a user may manually insertthe one or more serrated aperture stops 304 into the illumination arm110 or collection arm 112 of the inspection system 300. Alternatively, auser may manually remove the one or more serrated aperture stops 304from the illumination arm 110 or the collection arm 112 of theinspection system 300.

In another aspect, the one or more serrated apertures 306 of theserrated aperture assembly 302 may have a selected orientation. In thisregard, the orientation of the pattern formed by the one or moreserrated features 308 is such that the diffraction resulting from theone or more serration features 308 (e.g., teeth) misses the imagingportion (e.g., CCD chip) of the detector 104. In one embodiment, asshown in FIG. 3D, the serrate aperture 306 having serrated features 308as shown in FIG. 3B may generate diffraction orders along the horizontaldirection 310. As such, in this serration feature 308 configuration, itis advantageous to place the imaging portion of the detector 104 suchthat the long axis is orientated vertically, as shown in FIG. 3E,thereby allowing the imaging portion of the detector 104 to avoid thegenerated diffraction orders.

In another embodiment, as shown in FIG. 3F, the serration features 308may be positioned about the aperture 306 in a radial fashion, with theaperture 306 truncated at the horizontal edges. As shown in FIG. 3G, thetruncation of the aperture 306 at the horizontal edges, allows thediffracted light to avoid the imaging portion of the detector 104.

In a further embodiment, the truncation as depicted in FIG. 3F may beaccomplished utilizing additional opaque substrates (e.g., opaqueplates) arranged to block a selected portion of the aperture 306.Further, the amount of truncation to impart to the aperture 306 may beselectable utilizing one or more actuation stages (e.g., motorizedtranslation stage) in communication with a control system suitable forselectably controlling the actuation stage. For example, the controlsystem used to control the truncation of the aperture 306 may consist ofthe control system 114 described previously herein.

FIGS. 4A-4F illustrate an inspection system 400 equipped with one ormore Fourier filters 402 having blocking elements 410 with edgeapodization, in accordance with one embodiment of the present invention.

The present embodiment is directed to a Fourier filter 402 including oneof more blocking elements 410, whereby each blocking element isselectable to have a variable transmittance to illumination between 0and 100%. In this manner, the blocking elements of the Fourier filterinclude edge regions that selectively block illumination using patternsproviding graduated on/off filtering (as opposed to abrupt on/offfiltering). Application of the edge apodized Fourier filter 402 of thepresent invention in the imaging path of the inspection system 400 actsto reduce edge ringing and the diffraction tails associated withpatterns on the sample 106.

It is recognized herein that the components and embodiments ofinspection system 100 and 300 described previously herein should beinterpreted to extend to inspection system 400 unless otherwise noted.In this sense, the inspection system 400 includes an illumination source102 configured to illuminate a surface of a sample 106 disposed on asample stage 108, a detector 104 configured to detect light emanating(e.g., scattered) from defects from the surface of the sample 106.Further, the illumination source 102 (e.g., broadband source ornarrowband source) and the detector 104 are optically coupled via anoptical pathway 109 of an optical system 111. It is further noted thatthe Fourier filter 402 of the present invention may be implemented in aDF or BF inspection system setting.

In one aspect, the system 400 includes a Fourier filter 402 disposedalong the optical pathway 109 of the optical system 111. In oneembodiment, the Fourier filter 402 is disposed along the collection arm112 of the inspection system 400. For example, the Fourier filter 402may be disposed at the Fourier plane of the collection arm 112 of theinspection system 400. In this embodiment, the Fourier filter 402 ispositioned at or near the imaging aperture of the collection arm 112. Inthis regard, the Fourier filter 402 is configured to block illuminationreflected and/or diffracted from periodic features of sample 106.

In an alternative embodiment, the Fourier filter 402 may be disposedalong the illumination arm 110 of the inspection system 400 (not shown).

In one aspect, the Fourier filter 402 of inspection system 400 includesone or more blocking elements 410 arranged in an array pattern in orderto block a portion of illumination emanating from periodic structures ofthe surface of the sample. In one embodiment, the array pattern is aone-dimensional array. For example, the array pattern may include aseries of parallel rectangular elements (or stripes) arranged toselectively block illumination from the surface of the sample 106. Inone embodiment, the array pattern is a two-dimensional array (notshown). For example, the array pattern may include a rectangular arrayof blocking elements arranged to selectively block illumination from thesurface of the sample 106.

In a further aspect, the one or more blocking elements 410 of the arraypattern are arranged to block illumination diffracted or reflected fromone or more periodic structures on the sample 106. In an additionalaspect, the one or more blocking elements 410 of the array pattern arearranged to allow transmission of illumination scattered from one ormore defects on the sample 106 via the transmission regions 408 of thefilter 402.

The construction, positioning, and implementation of Fourier filters isdescribed generally in U.S. Pat. No. 7,397,557, issued on Jul. 8, 2008;U.S. Pat. No. 6,020,957, issued on Feb. 1, 2000; U.S. Pat. No.7,869,020, issued on Jan. 11, 2011; and U.S. Pat. No. 7,940,384, issuedon May 10, 2011, which are each incorporated herein by reference intheir entirety.

In an additional aspect, each of the one or more blocking elements 410of the Fourier filter 402 includes one or more edge regions configuredto provide a graduated transmission function to the illuminationtransmitted/block by the filter 402. The graduated edge regions of theblocking elements 410 are constructed to reduce the measuredcontribution from diffraction from patterned regions of the sample 106and/or suppress ringing artifacts. In this regard, the edge regions ofthe blocking elements 410 provide for a gradual transition from asubstantially 100% blocking state (e.g., center of blocking element) toa substantially 100% transmission state (e.g., center of transmissionregion 408). In a further embodiment, the particular configuration ofthe edge region results in a locally averaged transmission function ofthe Fourier filter that is an apodizing function.

In one embodiment, the edge region (shown by 406 in FIGS. 4A and 4B) mayinclude a variable dot density pattern 412. In a further embodiment, thevariable dot density pattern 412 may include a pattern of opaquefeatures (e.g., dots, squares, and the like) that vary in size as afunction of distance away from the fully opaque portion of the blockingelement 410.

In this sense, the variable dot density pattern 412 may consist ofalternating high and low transmittance areas, with the size of each lowtransmittance area (i.e., opaque features) shrinking as a function ofdistance from the blocking element until a region 408 of substantially100% transmittance is attained. In another embodiment, the variable dotdensity pattern 412 may have a selected pitch. In a further embodiment,the pitch of the variable dot density features is selected (e.g., smallenough) such that the diffraction orders resulting from the applicationof the filter 402 reside outside of the imaging field of view of thedetector 104, thereby avoiding, or at least reducing, optical artifactsin the image plane. In another embodiment, the width and apodizationprofile are selected in a manner to at least partially suppress sidelobes of the diffracted illumination without deteriorating the energyand width of the primary lobe. It is further noted herein the apodizingfunction of the filter 402 may consist of a superset of the locallyaveraged transmission function defined by alternating high transmittanceareas and substantially opaque areas.

In another embodiment, a given blocking element 410 may be apodizedalong a first direction (e.g., X) and a second direction (e.g., Y). Inthis regard, the blocking element 410 may include a first edge regionaligned on a horizontal portion of the blocking element 410 and a secondedge region aligned on a vertical portion of the blocking element 410.In this sense, the first region may include a variable dot densitypattern having a first selected pitch, while the second region includesa second variable dot density pattern having a second selected pitch.

In another embodiment, a variable dot density pattern may be formed bypatterning an optically opaque thin coating on the surface of atransparent mechanically stable substrate. It is recognized herein thatthe variable dot density pattern may be formed using any patterningtechnique known in the art, such as, but not limited to, lithographicprinting (e.g., e-beam lithography, optical lithography, or interferencelithography). Alternatively, the variable dot density pattern of theFourier filter 402 may be formed using patterned UV curable ink ordirect laser writing. In another embodiment, the variable dot densitypattern may be formed with one or more selectively reflective MEMsdevices, whereby transmission/opaque regions are formed using thetransmission/reflection elements of an MEM device.

In an alternative embodiment, the edge region (shown by 406 in FIGS. 4Aand 4B) may include a graded coating 414 having a thickness orcomposition gradient as a function of distance from the one or moreblocking elements 410. In a further embodiment, the graded film isconfigured to provide an apodizing function as described previouslyherein. For example, the thickness of the coating may become thinner asa function of distance from the one or more blocking regions 410,thereby resulting in an edge region with diminishing opaqueness as afunction of increasing distance from the blocking regions 410, until asubstantially transparent region 408 is attained. By way of anotherexample, the composition of the coating may be such that the coatingbecomes increasingly transparent as a function of increasing distancefrom the one or more blocking regions 410, thereby resulting in an edgeregion with diminishing opaqueness as a function of increasing distancefrom the blocking regions 410, until a substantially transparent region408 is attained. The graded coating may be deposited using any thin filmcoating technology known in the art, such as, but not limited to,sputtering deposition or evaporation.

In one embodiment, the Fourier filter with edge apodization 402 may beformed by depositing a metal onto a glass substrate. Any metal and anysubstrate known in the art may be used to form the Fourier filter of thepresent invention. For example, the Fourier filter with edge apodization402 may be formed by depositing chrome (e.g., depositing dot array ordepositing graded coating) on a glass substrate.

In another embodiment, in the case of the variable dot pattern of FIG.4D, the array may be configured to apply a half-wave cosine transmissionprofile given by:

${T_{c}(x)} = {\frac{1}{2}\left( {1 - {\cos\frac{\pi\; x}{L}}} \right)}$

where Tc is the transmission profile and x is the position along theapodization length, L. In a further embodiment, the fill factor for theapodized edge may consist of the following:

$\frac{{Area}_{m}(x)}{{Area}_{T}} = {1 - \sqrt{\frac{1}{2}\left( {1 - {\cos\frac{\pi\; x}{L}}} \right)}}$

where Area_(m) is the area of the metal opaque features (e.g., chromefeatures) and Area_(T) is the total cell area.

The total apodization length may take on various lengths. For instance,the length may range from approximately 100 to 1000 μm. The pitch of theopaque features in the variable dot density pattern may take on varioussizes. For instance, the pitch of features may range from approximately1 to 10 μm. The size of individual opaque features may also take onvarious sizes, ranging from 0.1 to 10 μm. The step size with whichadjacent opaque features varies may be on the order of 0.05 to 1 μm. Itis noted herein that the above transmission profile and dimensions arenot in any way limiting and should be interpreted merely asillustrative.

In another embodiment, the Fourier filter 402 with edge apodization maybe selectably inserted into the optical pathway 109 of the inspectionsystem 400. In this regard, the Fourier filter 402 is selectablyactuatable along a direction substantially perpendicular to the opticalpathway 109. In one embodiment, the Fourier filter 402 is disposed on anactuation stage (not shown) (e.g., translation stage and/or rotationalstage) suitable for selectably placing the Fourier filter 402 into thecollection arm 112 of the inspection system 400. In this regard, acontrol system may be communicatively coupled to the actuation stage andconfigured to selectably control the placement of the Fourier filter402. For example, the control system used to control the filtering andapodization imparted by the Fourier filter 402 may consist of thecontrol system 114 described previously herein.

In another embodiment, the Fourier filter 402 is disposed on a slidablestage (not shown) (e.g., translation stage and/or rotational stage)suitable for selectably placing the Fourier filter 402 into the opticalpathway 109 (e.g., collection arm 112) of the inspection system 400. Inthis regard, a user may manually insert the Fourier filter 402 into theimaging system of the inspection system 400. Alternatively, a user maymanually remove the Fourier filter 402 from the imaging system of theinspection system 400.

All of the methods described herein may include storing results of oneor more steps of the method embodiments in a storage medium. The resultsmay include any of the results described herein and may be stored in anymanner known in the art. The storage medium may include any storagemedium described herein or any other suitable storage medium known inthe art. After the results have been stored, the results can be accessedin the storage medium and used by any of the method or systemembodiments described herein, formatted for display to a user, used byanother software module, method, or system, etc. Furthermore, theresults may be stored “permanently,” “semi-permanently,” temporarily, orfor some period of time. For example, the storage medium may be randomaccess memory (RAM), and the results may not necessarily persistindefinitely in the storage medium.

Although particular embodiments of this invention have been illustrated,it is apparent that various modifications and embodiments of theinvention may be made by those skilled in the art without departing fromthe scope and spirit of the foregoing disclosure. Accordingly, the scopeof the invention should be limited only by the claims appended hereto.It is believed that the present disclosure and many of its attendantadvantages will be understood by the foregoing description, and it willbe apparent that various changes may be made in the form, constructionand arrangement of the components without departing from the disclosedsubject matter or without sacrificing all of its material advantages.The form described is merely explanatory, and it is the intention of thefollowing claims to encompass and include such changes.

What is claimed:
 1. An inspection system with selectable apodization,comprising: an illumination source configured to illuminate a surface ofa sample disposed on a sample stage; a detector configured to detect atleast a portion of light emanating from the surface of the sample, theillumination source and the detector being optically coupled via anoptical pathway of an optical system including an illumination arm and acollection arm; a selectably configurable apodization device disposedalong the optical pathway of the optical system, wherein the apodizationdevice includes two or more apodization elements operatively coupled toone or more actuation stages, the one or more actuation stagesconfigured to selectably actuate at least one of the two or moreapodization elements along one or more directions; a control systemcommunicatively coupled to the one or more actuation stages, wherein thecontrol system is configured to selectably apply a selected apodizationprofile to illumination transmitted along the optical pathway of theoptical system by controlling an actuation state of at least one of thetwo or more apodization elements, the selected apodization profileformed with the at least one of the two or more apodization elements. 2.The inspection system of claim 1, wherein the illumination sourcecomprises: at least one broad band illumination source.
 3. Theinspection system of claim 1, wherein the illumination source comprises:at least one narrow band illumination source.
 4. The inspection systemof claim 1, wherein the inspection system is configured as abright-field inspection system.
 5. The inspection system of claim 1,wherein the inspection system is configured as a dark-field inspectionsystem.
 6. The inspection system of claim 1, wherein the one or moreactuation stages of the selectably configurable apodization devicecomprises: one or more translational stages.
 7. The inspection system ofclaim 1, wherein the one or more actuation stages of the selectablyconfigurable apodization device comprises: one or more rotationalstages.
 8. The inspection system of claim 1, wherein the one or moreactuation stages of the selectably configurable apodization device areconfigured to selectably actuate one or more apodization elements intothe optical pathway of the optical system.
 9. The inspection system ofclaim 1, wherein the one or more apodization elements comprises: two ormore apodization elements.
 10. The inspection system of claim 1, whereinthe one or more apodization elements comprises: a single apodizationelement.
 11. The inspection system of claim 1, wherein the one or moreapodization elements operatively coupled to on one or more actuationstages comprises: a first apodization element disposed on a firstactuation stage and at least a second apodization element disposed on atleast a second actuation stage, wherein the control system is configuredto selectably control apodization of illumination transmitted along theoptical pathway of the optical system in one or more directions bycontrolling an actuation state of the first apodization element and anactuation state of at least a second apodization element.
 12. Theinspection system of claim 1, wherein the one or more apodizationelements comprise: one or more variable dot density apodizers.
 13. Theinspection system of claim 1, wherein the one or more apodizationelements comprise: one or more neutral density coating apodizers. 14.The inspection system of claim 1, wherein the one or more apodizationelements comprise: one or more serrated plates.
 15. The inspectionsystem of claim 1, wherein the one or more apodization elementscomprise: one or more Fourier filters having one or more blockingelements, the one or more blocking elements including one or moreapodized edges.
 16. The inspection system of claim 1, wherein the one ormore apodization elements are configured to apply a first selectedapodization profile along a first direction and at least a secondselected apodization profile along a second direction.
 17. Theinspection system of claim 1, wherein the selected apodization profilecomprises: at least one of a Gaussian profile, a cosine profile, and aSuper Gaussian profile.
 18. The inspection system of claim 1, whereinthe selected apodization profile is a function of one or more patternfeatures of the sample.
 19. An inspection system suitable for providingapodization, comprising: an illumination source configured to illuminatea surface of a sample disposed on a sample stage; a detector configuredto detect at least a portion of light emanating from the surface of thesample; an optical system including an optical pathway configured tooptically couple the illumination source and the detector; a serratedaperture assembly disposed along the optical pathway of the opticalsystem and configured as an aperture of the optical system, the serratedaperture assembly including two or more serrated aperture stops, whereinat least some of the two or more serrated aperture stops include aplurality of serration features, at least some of the two or moreserrated aperture stops including a serrated pattern having a selectedorientation; and a control system communicatively coupled to theserrated aperture assembly, wherein the control system is configured toselectably apply a selected apodization profile to illuminationtransmitted along the optical pathway of the optical system bycontrolling an actuation state of at least one of the two or moreserrated aperture stops, the selected apodization profile formed withthe at least one of the two or more serrated aperture stops.
 20. Theinspection system of claim 19, wherein the one or more serrated aperturestops comprise: one or more sheet metal plates including a serratedaperture.
 21. The inspection system of claim 19, wherein the one or moreserrated aperture stops comprise: one or more patterned metallicmaterial layers deposited on a transparent substrate forming a serratedaperture.
 22. The inspection system of claim 19, wherein the pluralityof serration features of one or more of the serrated aperture stops arearranged with a selected pitch.
 23. The inspection system of claim 22,wherein the selected pitch of the plurality of serration features of oneor more of the serrated aperture stops is a function of an aspect ratioof the detector.
 24. The inspection system of claim 22, wherein each ofthe plurality of serrations features has a selected size.
 25. Theinspection system of claim 19, wherein the serrated aperture assemblyincludes: two or more serrated aperture stops.
 26. The inspection systemof claim 25, wherein the two or more serrated aperture stops comprise: afirst serrated aperture stop; at least a second serrated aperture stopoperatively coupled to the first serrated aperture stop, wherein thefirst serrated aperture stop is oriented with respect to the at least asecond serrated aperture stop in order to achieve a selected pitch. 27.The inspection system of claim 25, wherein the two or more serratedaperture stops comprise: a first serrated aperture stop; at least asecond serrated aperture stop operatively coupled to the first serratedaperture stop, wherein the first serrated aperture stop is oriented withrespect to the at least a second serrated aperture stop in order toachieve the apodization profile.
 28. The inspection system of claim 19,wherein the serrated aperture assembly includes: a single aperture stop.29. The inspection system of claim 19, wherein the selected orientationof the serrated pattern produces diffraction orders substantially alonga first direction.
 30. The inspection system of claim 29, wherein anaxis of the detector is orientated along a second directionperpendicular to the first direction.
 31. An inspection system suitablefor providing apodization of illumination, comprising: an illuminationsource configured to illuminate a surface of a sample disposed on asample stage; a detector configured to detect at least a portion oflight emanating from the surface of the sample; an optical systemincluding an optical pathway configured to optically couple theillumination source and the detector, the optical pathway including anillumination arm and a collection arm; a Fourier filter disposed alongthe optical pathway of the optical system, wherein the Fourier filterincludes one or more illumination blocking elements arranged in an arraypattern, wherein the one or more illumination blocking elements arearranged to block a portion of illumination from the sample, wherein oneor more edge regions of the illumination blocking elements have agraduated transmission function, wherein a locally averaged transmissionfunction of the Fourier filter is an apodizing function.
 32. Theinspection system of claim 31, wherein the one or more edge regions aredefined by a variable dot density pattern.
 33. The inspection system ofclaim 32, wherein variable dot density pattern has a selected pitchalong at least one direction.
 34. The inspection system of claim 33,wherein the selected pitch along at least one direction of the variabledot density pattern is such that substantially all non-zero orderdiffraction orders reside outside of an imaging portion of the detector.35. The inspection system of claim 32, wherein variable dot densitypattern has a first selected pitch along a first direction and a secondselected pitch along a second direction.
 36. The inspection system ofclaim 31, wherein the one or more edge regions are defined by a thinfilm coating having a transmittance gradient.
 37. The inspection systemof claim 31, wherein the one or more blocking elements of the Fourierfilter are arranged to block light from periodic structures of thesample.
 38. The inspection system of claim 31, wherein the one or moreblocking elements of the Fourier filter are arranged to transmit lightfrom non-periodic structures of the sample.
 39. The inspection system ofclaim 31, wherein the one or more blocking elements are arranged in aone-dimensional array.
 40. The inspection system of claim 31, whereinthe one or more blocking elements are arranged in a two-dimensionalarray.
 41. The inspection system of claim 31, wherein the Fourier filteris positioned in the collection arm of the optical system.
 42. Theinspection system of claim 31, wherein the Fourier filter is positionedat the Fourier plane of the collection arm of the optical system. 43.The inspection system of claim 31, wherein the Fourier filter ispositioned at the Fourier plane of the illumination arm of the opticalsystem.
 44. A system for providing selectable apodization in an opticalsystem, comprising: a selectably configurable apodization devicedisposed along the optical pathway of the optical system, wherein theapodization device includes two or more apodization elements operativelycoupled to one or more actuation stages, the one or more actuationstages configured to selectably actuate at least one of the two or moreapodization elements along one or more directions; and a control systemcommunicatively coupled to the one or more actuation stages, wherein thecontrol system is configured to selectably apply a selected apodizationprofile to illumination transmitted along the optical pathway of theoptical system by controlling an actuation state of at least one of thetwo or more apodization elements, the selected apodization profileformed with the at least one of the two or more apodization elements.